Behavior of chloride during coal combustion in an AFBC system

Two 1000-h burns were conducted with the 12-in. (0.3 m) laboratory AFBC sys tem at Western Kentucky University. Operating conditions similar to those u sed at the 160-MW AFBC system at the TVA Shawnee Steam Plant located near P aducah, KY, were used. A low-chlorine (0.012% Cl and 3.0% S) western Kentuc ky Na. 9 coal and a high-chlorine (0.28% Cl and 2.4% S) Illinois No. 6 coal were used in this study. Four different metal alloys [carbon steel C1020 ( 0.18% C and 0.05% Cr), 304 SS (18.39% Cr and 8.11% Ni), 309 SS (23.28% Cr a nd 13.41% Ni), and 347 SS (18.03% Cr and 9.79% Ni)] were exposed uncooled i n the freeboard area at the entrance to the convective pass, where the meta l temperature was approximately 900 K. A two-phase investigation was carrie d out in order to study the fate of chlorine during coal combustion in an A FBC system and to study the susceptibility of boiler components to corrode in combustion gases containing hydrogen chloride. As determined from emissi on and ash studies, the temperature in an AFBC system plays a key role in t he retention of chloride, which is more favorable at low operating temperat ures. A small amount of scale failure was observed on the other three sampl es in both test runs. On the basis of the SEM-EDS mapping results, there wa s no localized chloride distribution observed on the surface of the coupons , either in the scale failure area nor on the rest of the metal part. Some trace amount of chloride was found but was evenly distributed on the surfac e of the coupons. There was no concentration of chloride on the spot of sca le failure. The scale failure might be due to sulfur attack and/or the effe ct of erosion. Further study with higher chlorine-content coals for more co nclusive information is needed.